The present invention relates to an image scanner which employs an image sensor such as pickup elements, and more particularly, to a moire removing device for use in the image scanner.
Generally, in an image scanner, an original image is subdivided into a plurality of pixels, and each of the pixels are optically focussed on an optical sensor for the image read out operation. In a conventional image scanner, when reading a dot printed original image or a fine continuous pattern original image, a lens is disposed in a position for providing an intentionally defocused image so as to lower the spatial frequency of the image of the original on the image sensor in order to avoid generation of moire. Alternatively, image processing unit is additionally provided to remove the moire.
However, if the lens is defocused, resolution is lowered even when the spatial frequency of the image is low and the image may encounter Moire. Therefore, the defocusing would be disadvantageous for reading such images. On the other hand, if the Moire is to be removed by means of the image processing unit, extremely complicated proceedings have to be executed. Further, extremely long periods of time are required if a CPU is used for the processing. An electronic circuit may be available for performing the image processing within a short period of time. However, a large number of components may be required for constituting the electronic circuit.